Thermionic tube control



April 1937- v. TAR'ZIAN 2,076,102

THERMIONIC TUBE CONTROL Filed March 1.4, 1935 2 Sheets-Sheet l 4-, I; i, w ,4

, k J HGURE'EI- I FIGUREI.

INVENTDR April 6, 1937. V. TARZIANI 2,076,102

THERMIONIC TUBE CONTROL I Filed March 14, 1935 2 Sheet-Sheet 2 INVENTDR Patented Apr. 6, 1937 v UNITED STATES PATENT OFFICE Claims.

This invention is related-to the control of the sensitivity of thermionic tubes. More specifically my invention may be used to control the volume of radio receivers.

5 One of the objects of my invention is to control the sensitivity of a thermionic tube without altering the direct current voltages employed in connection with the tube. Another object is to remotely control the sensitivity of an audio am- 0 plifier tube. A further object will be found in adaptation of a volume control which may be connected to an existing radio receiver without altering the existing connections. A still further objectis in the rapid variation from minimum to maximum adjustment of volume without intermediate positions or de-energizing any of the thermionic tubes employed.

Figure I shows one form of my invention.

Figure II shows a modification of my invention.

Figure III is a schematic wiring diagram illustrating the circuit employed in Figure I.

Figure IV is a diagram of a modified circuit arrangement similar to Figure III but showing the volume control circuit connected between screen grid and anode.

{ Figure V is a diagram of another modification of Figure III in which the volume control circuit is connected between unipotential cathode and anode.

Figure VI is a circuit diagram of a push pull amplifier in which the volume control circuit is connected between the control grid electrodes.

Figure VII is a circuit diagram of a push pull amplifier in which the volume control circuit is connected between the anode electrodes.

In Figure I, a radio receiving set, including the radio frequency amplifying and detecting tubes is represented by I. The output of l is connected to an audio frequency amplifying system 2. Theamplified currents from I may be reprol duced by a loudspeaker, such as 3.

The socket for the output tube is 4. In the audio amplifier 2 there may be inserted, by way of example, an output tube such as RCA 47. The

tube is shown as 5. The control grid of tube 5 is represented asconnected to prong B and the screen grid to prong 1. Two small metal washers just fitting the prongs are used to connect the leads 8 and 9 to the prongs 6 and 1. The washers are of small diameter and the connecting leads are insulated to avoid short circuits between the various prongs or the prongs and ground. The 55 tube 5 is inserted in socket 4, and 6 and I make firm connections with the washers when the tube is pressed into position.

The lead 9 is connected to a fixed condenser ID. The condenser I0 should have a relatively low reactance to audio frequency currents and may be of the orderof .5 to 2 microfarads. The lead 8 is connected to snap switch II. The snap switch in turn connects to condenserlll. When the switch 1 I is open, tube 5 operates at its maximum amplifying characteristic. When switch 10 II is closed, the control grid 6 is connected to the screen grid 1. Since the screen grid is practically at ground for audio currents, the control grid connected to it, is practically grounded and the tube is at zero or a minimumresponse. 15 The closing of switch ll, while it acts as a substantial short circuit on the tube, does not short circuit the direct current potentials because condenser I0 is an open circuit for direct current.

The connections shown in Figure I are particularly suitable for a filament type output tube. I do not recommend connections from control grid to filament because, I have found such connections put alternating currents on the control grid, when the filament is heated from alternating current. The connections may also be from plate to screen grid but I prefer screen grid to control grid, because a smaller condenser is required.

In Figure II, I have shown my invention applied to a heater type pentodeoutput tube. The 30 connection may be to cathode instead of ground in aheater type tube such as the RCA 42. The connection I prefer in the case of a push pull audio amplifying system is from control grid of one tube to the control grid of the other through 3:" a capacity such as l3, or even without this capacity as generally the grids are at the same D. 0. potential. The connection in push pull or class B operation can also be from plate to plate of the output tubes. 40

v In Figures II to VII similar reference numerals will indicate similar elements. In Figure II the secondary 20 of an audio input transformer 2| has a terminal connected to control grid 22 and the other terminal grounded at 23. The indi- 45 rectly heated cathode 24 is grounded through self bias resistance 25 and by-passed by capacity 26. The cathode 24 is heated by filament 21 which may be energized by transformed alternating current or any suitable source; such as, a 50 battery 28. The anode 29 is connected through loud speaker 30 or the like, to the positive terminal of the B battery 3|. The negative terminal of theB battery is grounded. The B battery may be by-passed by capacity 32. The screen grid 33 is connected to the positive terminal of B battery 3|. The volume control circuit of my invention is represented by a suitable lead l2 which is connected from grid 22 to low impedance capacity 5 l3, switch l4, and lead l5 to cathode 24.

In Figure III the circuit arrangements are illustrated which may be used in connection with Figure I. In Figure III a filament type cathode 34 is used. The cathode is energized from an alternating current source 35. Across 34 is connected a resistance 36. The center of this resistance is grounded through self-bias resistance 25. A suppressor grid 31 is connected to the filament. The volume control circuit is connected by lead l2 to low impedance capacity l3, thence to switch It, and lead IE to the screen grid 33.

The reference numerals 9, l0, H, and 8 of Figure I correspond respectively to numerals I 2, l3, l4 and I5 of Figures II to VII.

Figure IV resembles Figure III and is only modified in two respects. The first distinction is that the suppressor grid 3! is omitted from Figure IV. The second distinction is that the volume control circuit I2, l3, l4 and I5 is connected between 25 anode 29 and screen 33.

Figure V diifers from Figure II only in that the volume control circuit I2, I3, [4 and [5 of Figure V is connected between anode 29 and cathode 21.

30 Figures VI and VII are well known push pull circuits. The power source is represented as C battery 40, A battery 4| and B battery 42. The amplifier tubes 43 and 44 have their control grids 45 and 46 connected to the input transformer 41.

35 The anodes 48 and 49 are connected to the output transformer 50. Although the tubes are shown as triodes, it should be understood that pentodes or other multi-electrode tubes may be used. In Figure VI, the volume control circuit I2, l3, I4

40 and I5 is connected between grids 45 and 46. In

Figure VII, the volume control circuit is connected between anodes 48 and 49. The operation of each circuit is similar. In the circuit of Figure VI the input circuit is practically short circuited for audio frequency by the connection of the low impedance capacity of the volume control circuit.

It will be evident that my invention as described may be employed in any of the commer- 5 cial radio receivers employing thermionic audio amplifiers without altering their present connections. One convenient method of utilizing my invention is to quickly and easily cut the audio gain of a radio receiver from a remote point.

5 I have found that the connections I propose may be applied to the final audio stage of a radio receiver and extended to convenient points about the room without having an adverse effect on the quality of reproduction.

60 A gain switch may be convenient to the listeners chair to quickly eliminate undesirable advertising or sales talks. While the gain is quickly reduced to zero the snap switch may equally quickly restore the receiver to its normal or max- 5 imum gain to allow the listener to get the enjoyable parts of the program. The switch may be usefully employed near the telephone. It should be understood that several switches may be used in parallel provided they are normally open cir- 7 cuited. I also contemplate that a time switch may be used in place of a snap switch. The time switch may be adjusted to a short circuit interval equal to the average period of undesirable advertising or sales talks. In this manner the user 75 could manually cut the gain and the full amplification would be automatically restored after a lapse of a minute or any other desired interval.

I claim.

1. A thermionic tube control comprising a thermionic tube having an electrode at substantially ground potential to audio frequency currents, a control grid and at least one other electrode, a connection from said control grid to a capacity whose reactance to audio frequency currents is substantially equal to a short circuit and high resistance to direct currents, a connection from said capacity to a switch, and a connection from said switch to a point which has substantially ground potential with respect to incoming signal representing currents, and is not subject to potential variations due to filament heating alternating currents.

2. A remote gain control connection for an audio amplifier including a thermionic tube having a control grid, an indirectly heated cathode, and plate electrodes, a switch, a capacity whose reactance to audio frequency currents is substantially equal to a short circuit, and means for serially connecting said switch and said capacity between said control grid and said indirectly heated cathode, and a pair of flexible leads for positioning said switch at a point remote from said audio amplifier.

3. A remote gain control connection for a push pull audio amplifier, including thermionic tubes each having control grid, cathode and anode electrodes, a switch for connecting between said control grids a capacity whose reactance to audio frequency currents is substantially equal to a short circuit, and flexible leads for positioning said switch at a point remote from said audio amplifier.

4. A remote gain control connection for an audio amplifier including a thermionic tube hav-v ing prongs connected to its control grid, indirectly heated cathode and plate electrodes, a fiat washer-like connection frictionally engaging the prong connecting to said control grid, a capacity whose reactance to audio frequency currents is substantially equal to a short circuit connected to said connection and a switch connecting said capacity to the indirectly heated cathode prong of said tube.

5. A remote gain control for themiionic tubes comprising a capacity whose reactance to audio frequency currents is substantially equal to a short circuit, a thermionic audio amplifier tube having control grid, cathode and plate electrodes and a prong type base and connections from said electrodes to said prongs, detachable means, connections between said detachable means and said control grid and cathode prongs, and connections to said detachable means including switching means for connecting or disconnecting said capacity between said control grid and cathode prongs.

6. A remote gain control connection for an audio amplifier including a thermionic tube having a control grid, cathode and plate electrodes, a switch for connecting a capacity whose reactance to audio frequency currents is substantially equal to a short circuit between said plate and cathode, and a pair of flexible leads for pcsitioning said switch at a point remote from said audio amplifier.

7. A remote gain control connection for a push pull audio amplifier, including thermionic tubes each having control grid, cathode and anode electrodes, a capacitor, a switch for serially connecting said capacitor and said control grids,

and flexible leads for positioning said switch at a point remote from said audio amplifier.

8. A thermionic tube control comprising a thermionic tube having a control grid, a cathode at substantially ground potential to audio frequency currents, and anode electrodes; a switch, a capacity, whose reactance to audio frequency currents is substantially equal to a short circuit; a connection from said control grid to said capacity and from said capacity to said switch; and a connection from said switch to a point which has substantially ground potential with respect to incoming signal representing currents 9. In an audio frequency amplifier system employing thermionic tubes, for amplifying alternating currents, a source of alternating current, a control for said amplifier which comprises a, connection from one point in said system to a capacity, whose reactance to audio frequency currents is substantially a short circuit, and a connection from said capacity to a switch and from said switch to another point in said amplifier system whose instantaneous alternating current potential is opposite to the first named point.

10. A thermionic tube control comprising a thermionic tube having control grid, cathode and anode electrodes, a source of alternating current connected between said control grid and cathode electrodes, a connection from one of said electrodes thru a capacity, whose reactance to audio frequency currents is substantially equal to a short circuit, to a switch and from said switch effectively to another of said electrodes whose instantaneous alternating current potential is opposite to the first of said electrodes.

V'ERAGE TARZIAN. 

